The 'Ama'u fern is unique to Hawai'i and can be found in shady areas from sea level all the way up to 7,000 ft. The fern can vary in size from young ferns only a foot or so high, to adult ferns that have fronds over 10 feet long. Many 'Ama'u ferns can be found in Volcano Village and the Hawai'i Volcanoes National Park.

The trunks of the 'Ama'u resemble that of the Hāpu'u fern in that it has a golden-orange, soft, velvety hair, or pulu, that was used in the past as a stuffing for pillows and mattresses. However, the fronds themselves look different from Hāpu'u and have a unusual unfurling pattern and twice divided leaves. The young 'Ama'u fronds are reddish colored and turn to the more familiar green once they age.